Electric arc furnace apparatus having a shaped magnetic field for increasing the utilized area of the arcing surface of an electrode and improving the heating efficiency

ABSTRACT

The unit heat flux to a fluid-cooled electrode and the heat flux to the material being heated by a diffused arc column operating at a given electric current level are controlled by a magnetic field coaxial with the electrode, part of the flux lines of which pass through both the arcing surface of the electrode and the molten bath. The magnetic field pattern at the electrode and near the electrode is shaped into desired configurations to accomplish the purposes of the invention by the use of high permeability material in the electrode in some embodiments, and permanent magnets in the electrode in other embodiments. Where high permeability material is employed, the material may form part of the electrode tip and be substantially symmetrical around the inside and outside diameter of the tip, or may be so proportioned as to provide an outside diameter biased electrode tip. The tip may be constructed of copper and high permeability material disposed within the tip either in the form of a short ring, or axially and radially extending material occupying a substantial portion of the volume of the tip and the supporting column. Where a permanent magnet is employed, it is disposed in the tip, and the north and south poles of the permanent magnet may be axially disposed with respect to each other with their axis parallel to the axis of the electrode. The poles of the permanent magnet are selectively in opposition to a field set up in the furnace by a solenoid, or selectively in polarity adding to the field set up in the furnace by the solenoid. Additionally, the permanent magnet may have its north and south poles lying perpendicular to the axis of the electrode. Selectively, the north pole of the permanent magnet may be on the side thereof adjacent the axis of the electrode, or may be on the side thereof farthest from the axis of the electrode, nearer to the wall of the furnace and nearer to the solenoid setting up a magnetic field within the furnace.

United States Patent [191 Kolano [451 Jan. 1,1974

[ 1 ELECTRIC ARC FURNACE APPARATUS HAVING A SHAPED MAGNETIC FIELD FORINCREASING THE UTILIZED AREA OF THE ARCING SURFACE OF AN ELECTRODE ANDIMPROVING THE HEATING EFFICIENCY Frank J. Kolano, North Braddock, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: Sept. 22, 1972 211 Appl. No.: 291,470

[75] Inventor:

Primary Examiner-Roy N. Envall, Jr. Attorney-A. T. Stratton et al.

[57] ABSTRACT The unit heat flux to a fluid-cooled electrode and theheat flux to the material being heated by a diffused arc columnoperating at a given electric current level are controlled by a magneticfield coaxial with the electrode, part of the flux lines of which passthrough both the arcing surface of the electrode and the molten bath.The magnetic field pattern at the electrode and near the electrode isshaped into desired configurations to accomplish the purposes of theinvention by the use of high permeability material in the electrode insome embodiments, and permanent magnets in the electrode in otherembodiments. Where high permeability material is employed, the materialmay form part of the electrode tip and be substantially symmetricalaround the inside and outside diameter of the tip, or may be soproportioned as to provide an outside diameter biased electrode tip. Thetip may be constructed of copper and high permeability material disposedwithin the tip either in the form of a short ring, or axially andradially extending material occupying a substantial portion of thevolume of the tip and the supporting column. Where a permanent magnet isemployed, it is disposed in the tip, and the north and south poles ofthe permanent magnet may be axially disposed with respect to each otherwith their axis parallel to the axis of the electrode. The poles of thepermanent magnet are selectively in opposition to a field set up in thefurnace by a solenoid, or selectively in polarity adding to the fieldset up in the furnace by the solenoid. Additionally, the permanentmagnet may have its north and south poles lying perpendicular to theaxis of the electrode. Selectively, the north pole of the permanentmagnet may be on the side thereof adjacent the axis of the electrode, ormay be on the side thereof farthest from the axis of the electrode,nearer to the wall of the furnace and nearer to the solenoid setting upa magnetic field within the furnace.

10 Claims, 10 Drawing Figures LJJ llllll' lllll [I PATENTEDJAN H974SHEEI 10F 3 FIG. 18.

FIG.

PRIOR ART PRIOR ART ELECTRIC ARC FURNACE APPARATUS HAVING A SHAPEDMAGNETIC FIELD FOR INCREASING THE UTILIZED AREA OF THE ARCING SURFACE OFAN ELECTRODE AND IMPROVING THE HEATING EFFICIENCY CROSS REFERECNE TORELATED APPLICATION Certain inventions related tothose disclosed in thepresent application are disclosed and claimed in copending application,Ser. No. 291,433, filed concurrently by Ronald R. Akers, and assigned tothe same assignee as the present application.

FIELD OF THE INVENTION The invention relates to an electric arc furnacehaving an electrode and a solenoid adjacent the wall of the furnace forsetting up amagnetic field in the furnace around the electrode, withinthe melt, and between the electrode and the melt, and in which theelectrode contains means for shaping the magnetic field of the solenoidat or near the tip of the electrode to obtain operating advantages.

- DESCRIPTION OF THE PRIOR ART It is old in the art to employ highpermeability mate- 'rial in an electrode to provide a low reluctancepath for lines of a magnetic field. Sucha general arrangement isdescribed and claimed in US. Pat. No. 3,395,239, issued July 30, 1968 toA. M. Bruning et al for Arc Furnace Electrode and Magnetic CircuitForming Structure for Use Therein, assigned to the assignee of theinstant invention.

It is old in the art to employ permanent magnets located in an electrodefor setting up a magnetic field adjacent the arcing surface thereof toexert a force on the arc and cause the arc to move around the arcingsurface. A permanent magnet in the form of a ring with its axisextending parallel to the axis of the electrode and having the insideand outside surfaces of the ring forming the north and south magneticpoles of the magnet so that the poles lie in a direction perpendicularto the axis of the electrode is described and claimed in the copendingapplication of S. M. DeCorso et al. for fluid cooled electrode havingpermanent magnets to drive the arc therefrom and apparatus employing thesame, Ser. No. 4488, filed Jan. 21, 1970, the above-identified copendingapplication being assigned to the assignee of the instant invention.

Suggestions as to the use of a permanent magnet in an electrode alsooccur elsewhere in the patented prior art. In the past a form of furnacein which two electro magnetic field producing means are used to controlan arc has been, used. The specific form used comprises a furnaceincluding a relatively short electrode tip electromagnet having 3,200ampere turns of energizing force available and an external solenoidhaving 5,040 ampere turns of bucking or opposing magnetic forceavailable. The magnetic forces involved were specifically arranged tocancel at the centerline of the electric arc furnace in which thisapparatus was being used. The relative distances between the sources ofmagnetic energy or the generators of magnetomotive force were such thatthe net electric field adjacent the electrode tip was relatively strongeven though the magnetomotive force generated by the electrode tipelectromagnet was relatively smaller than the magnetomotive forceproduced by the solenoid. This caused a relatively constrainedcircumference of rotation for the arc. This may be useful in a furnacestartup condition where stirring is a more important function than it isat other times during a melting process such as when the melt has becomehot.

I SUMMARY OF THE INVENTION Furnace apparatus, preferably cylindrical,has an electrode mounted therein to form an arc to a melt and has asolenoid so disposed with respect to the electrode and the melt, theaxis of the solenoid being parallel to and preferably substantiallycoinciding with the axis of the electrode, that a magnetic field is setup in the furnace with magnetic field lines extending in the furnacesubstantially upward beyond the positionof the arcing surface of theelectrode and extending downward through the melt substantially lowerthan the surface of the melt, as well as through the space in thefurnace lying axially therein between the arcing surface and the meltsurface. There are several embodiments of the electrode which may beclassified in two general classes, a first class depending upon materialof high permeability contained or included within the electrode toprovide a low reluctance path and shape the magnetic field, or a secondgeneral class in which the electrode includes a permanent magnet toshape the total magnetic field. There are several embodiments in thefirst class, according to whether the electrode tip itself is made atleast in part of high permeability material, or whether the electrodetip is made of some other material such as copper and high permeabilitymaterial is included in the tip, or in the tip and/or the supportingcolumn for the tip. Certain preferred variations in the location of thehigh permeability material and the amount thereof give certain preferredshapings of the magnetic field set up by the solenoid to accomplishcertain desired results. In the second general class there are furthersubclasses depending upon whether the permanent magnet has its magneticpoles axially disposed in a direction parallel to the axis of theelectrode or whether the permanent magnetic has its opposite magneticpoles disposed in a direction generally perpendicular to the axis of theelectrode. Where the poles are axially disposed in a direction parallelto the axis of the electrode, the polarity of the permanent magnet maybe such that its field opposes of adds to the solenoid field, both ofsaid permanent magnetic in fields, said two polarity positions adding toor opposing the solenoid field giving different shaping of a total fieldincluding the solenoid field and each providing a desirable fieldshaping to accomplish certain objectives which are not necessarilymutually exclusive. While the permenent magnet in the tip in the form ofa ring with the outside surface of the ring of larger diameter formingone magnetic pole and the inside surface of smaller diameter of the ringformingthe other magnetic pole, the polarity may be selected so that anyparticular magnetic pole lies on the side of the electrode toward theaxis of the electrode and toward the axis of the solenoid field, or saidlast-named magnetic pole may lie on the side of the electrode away fromthe axis thereof and closer to the wall of the furnace and to the turnsof the solenoid, both of said magnetic pole configuration providingfield shapes which are different from each other, which are utilized toaccomplish certain objectives and the control of the are on the arcingsurface of the electrode, on the SLIXfaC Of the melt, and within theaxial space between the melt and the electrode tip, said objectives notnecessarily being exclusive of each other.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention reference may be had to the preferred embodiment exemplary ofthe invention shown in the accompanying drawings in which:

FIG. 1A illustrates the magnetic field set up by a solenoid in a furnacein the region adjacent an electrode and the region between an electrodeand a melt where the electrode neither sets up a magnetic field by meanscontained within the electrode nor contains or includes any means fordisturbing the normal field pattern set up by the solenoid;

FIG. 18 illustrates the magnetic field set up in a furnace by anelectrode containing a permanent magnet in which the poles of the magnetare axially disposed with respect to each other in a directioncorresponding to the axis of the electrode and where no solenoid fieldis present;

FIG. 2A illustrates the shaping of a solenoid field where the electrodetip is at least partially composed of high permeability material,portions of which are symmetrically locatedin the portion of the tipwhich has an inside diameter and the portion of the tip which has anoutside diameter;

FIG. 28 illustrates the shaping of a solenoid field where the electrodehas only a small portion of the total high permeability materialadjacent the inside wall of smaller diameter and a very large portion ofthe high permeability material in the inside wall of the tip and/orelectrode column forming the outside diameter and producing anoutside-diameter-biased electrode tip;

FIG. 2C illustrates the shaping of a solenoid field where the electrodetip and electrode supporting column are composed of diamagneticmaterial, the tip being composed, for example, of copper, and there isdisposed within the tip a ring relatively small thickness and ofrelatively small height composed of high penneability material; 7

FIG. 2D illustrates the shaping of a solenoid field where the electrodeincludes a massive volume of high permeability material having a greaterradial dimension than that of FIG. 2C and having a substantially greateraxial dimension than that of FIG. 2C;

FIG. 3A illustrates the shaping of the magnetic field where the tip andsupporting column of the electrode are composed of diamagnetic material,and there is located within the tip a permanent magnet with the polesthereof axially disposed with respect to each other in a directionparallel to the axis of the tip, and the polarity of the permanentmagnet is in the same direction as the polarity of the magnetic fieldgenerated by the solenoid so that in effect the magnetic fields of thesolenoid and the permanent magnet add;

FIG.'3B shows the shaping of the magnetic field of a solenoid where theelectrode has a tip supporting column composed of a diamagnetic materialwith a ringshaped permanent magnet located in the tip with its oppositepoles disposed with respect to each other axially in a directionparallel to the axis of the electrode, the permanent magnet being sopoled with respect to the field of the solenoid that the field of themagnet and the field of the solenoid oppose each other;

FIG. 4A shows the shaping of a solenoid field where the electrode tipand column are composed of diamagnetic or paramagnetic material and theelectrode has a permanent ring magnet located in the tip with the insidewall of smaller diameter of the magnet forming one magnetic pole and theoutside wall of larger diameter of the ring magnet forming the othermagnetic pole where the north magnetic pole of the field set up by thesolenoid is at the upper end of said field and the south magnetic poleof the ring magnet is on the inside of the ring magnet toward the axialcenter of the field generated by the solenoid; and

FIG. 4B shows the shaping of the solenoid field where the tip andelectrode column are composed of diamagnetic or paramagnetic material,where the tip has mounted therein a ring magnet with the inside wall ofsmaller diameter forming one magnetic pole and the outside wall ofsmaller diameter forming the other magnetic pole, where the northmagnetic pole of the solenoid is illustrated as being at the upper endthereof, and the north pole of the permanent ring magnet is on the sidethereof towards the axis of the magnetic field generated by thesolenoid.

DESCRIPTION OF PREFERRED EMBODIMENTS Particular reference is made toFIG. 1A. An electrode generally designated 10 has a supporting columnshown at 11 and a tip shown at 12 which is seen to be generally annularand generally U-shaped in crosssection and to have an annular spacetherein extending completely around the tip, the space being designated13. The wall of the furnace is shown at 15, the solenoid winding at 16the melt at 17 and magnetic field lines of the magnetic field set up bythe solenoid at 19. It will be understood that for convenience ofillustration only half of the electrodes and half of the furnace areshown, it being understood that the other half is generally symmetricalwith the half shown. For the present purposes of the description of FIG.1A, the field intensity at every point within the furnace need not bedescribed. The field intensity may be calculated according to formulascontained in many standard textbooks on Electrical Engineering, forexample, a work entitled Direct and Alternating Currents by E. A. Loew,2nd Ed., McGraw-I-Iill Co., Inc., 1938, pp. 67-72 inc. and pp. 81 and82.

The tip is also shown as having a generally U-shaped passageway thereinextending around the entire tip for the flow of cooling fluid to conductheat flux from the tip, the passageway being shown at 20 and providedfor reasons hereinafter to be described.

Particular reference is made to FIG. 1B in which it is assumed that thesolenoid 16 is not energized or is removed, so that there is nosolenoidal field present within the furnace and the only magnetic fieldcreated therein is produced by a permanent magnet 22 mounted within theelectrode tip and having its magnetic poles generally axially disposedwith respect to each other and producing a magnetic field having fieldlines 24.

It is to be noted in connection with FIG. 1A that certain of themagnetic field lines 19 extend in a substantially axial directionbetween the surface of the melt l7 and the electrode tip 12. The effectof such magnetic field linesis to tend to focus an are between theelectrode tip and the melt and to control the area of the surface of themelt on which the arc impinges. Somewhat similar use of a magnetic fieldis old in the art as exemplified for example by U.S. Pat. No. 2,978,525to H.

Gruber et al., issued Apr. 4, 1961 for Magnetic Field Coil forConcentrating the Arc in a Vacuum Arc Furnace. The prior art also showsa magnetic field coil around a furnace to enhance stirring of the melt.

With respect to FIG. IE, it is old in the art to have means disposed inan electrode tip for producing a magnetic field having a strong fieldcomponent transverse to at least large portions of the arcing surface ofthe electrode tip for exerting a force on an arc extending axially fromthe tip to cause the arc to move substantially continuously around thetip. Electrodes utilizing a magnetic field in the tip for this purposeare exemplified by US. Pat. No. 3,369,068 issued Feb. 13, 1968 to P. F.Kienast, and US. Pat. No. 3,385,987 issued May 28, 1968 to c. B. Wolfeet al., both of said patents being assigned to the assignee of theinstant invention.

Generally speaking the rotating or are moving effect of the magneticfields described in the afore-identified patents is similar to therotating effect of the magnetic field of magnet 22 in which the magneticpoles are axially disposed with respect to each other.

The magnetic field of FIG. 1B is seen to have some of the field linesextending between the arcing surface of the tip and the melt. The effectof these field lines is not only to focus the are on the melt but it.hasbeen found in. practice that if a magnetic field produced in the tipexceeds a certain strength, focusing of the arc at the tip may producethe undesirable result of concentrating the arc path over a very narrowtrack on the tip with the result that erosion of material from the tipis increased.

Particular reference is made now to FIG. 2A in which a magnetic field isset up within the furnace having wall by solenoid 16, and in which anelectrode generally designated 30 has a supporting column 31 and anannular tip 32 generally U-shaped in cross section with a space 33therein, the tip being at least largely composed of a high permeabilitymaterial indicated by the shaded material at 34. The lines of themagnetic field generated by solenoid 16 are shown at 36; it is seen thatthere is a concentration of field intensity at the bottom as indicatedby the' increase in the number of lines and the close spacing of thelines designated 36a. The advantages of a magnetic field configurationsuch as that' shown in FIG. 2A and its aficct upon arc operation andfurnace operation will be fully described hereinafter when the variousfield patterns of all of FIGS. 2A, 2B, 2C, and 2D, are stated andexplained fully with respect to each other.

Particular reference is made now to FIG. 28; an electrode generallydesignated 40 has supporting column 41 and a tip 42 with an annularspace 43, and the field lines of the magnetic field generated bysolenoid 16 are shown at 46. The portion of the tip and supportingcolumn composed of high permeability material is designated 44 and it isseen that the volume of high permeability material within the tip ismuch greater in the outsidewall portion thereof than it is in the insidewall portion thereof, and that high permeability material 44 may have aportion thereof 440 which extends axially well above the mean height ofthe tip and may be thought of as forming part of the supporting column.It is noted that there is a high concentration of magnetic fieldstrength between the tip and the melt, as indicated by lines 46a, andthat also magnetic field lines indicated by lines 46b may enter the tipon the outside surface thereof and other magnetic field lines indicatedby line 460 may extend from the melt to the inner wall of the arcingsurface of the tip. Particular reference is made now to FIG. 2C where anelectrode generally designated 50 has a supporting column 51 with a tip52 composed of diamagnetic material such as copper, in the annular space53 of which there is disposed a ring of high permeability material 54.The field lines of the magnetic field generated by solenoid 16 are shownat 56. It is to be noted that the radial dimension of ring 54 of highpermeability material is substantially less than the radial dimension oftip 32 of FIG. 2A of high permeability material, and the magnetic fieldlines 56a while concentrated in the area of the furnace between the tipand the melt are shown to converge as they approach the highpermeability material of the ring 54.

Particular reference is made now to FIG. 2D. Electrode generallydesignated 60 has a supporting column 61 with the tip 62 having anannular space 63 therein and mounted in the electrode and extending intothe space within the tip and extending a substantial distance axiallywithin the supporting column is a large mass of high permeabilitymaterial 64. The field lines of the solenoid are shown at 66. There is asubstantial increase in magnetic field strength between the tip and themelt as indicated by theincreased field lines 660 which converge towardseach other as they approach the lower end of the massive highpermeability material 64. There is an increase in magnetic fieldstrength at the side of the tip as indicated by magnetic field lines 66bwhich converge towards the massive high permeability material 64. Inaddition there is a substantial bending or pulling of other lines of thesolenoid field toward the mass of high permeability material asindicated by lines 660.

The uses and advantages of the various field configurations shown inFIGS. 2A through 2D inclusive may best be described with reference toprior art problems which the apparatus and processes of the instantinvention solve. It is well known that at low gas pressures, electricalcurrent can pass across a gap between electrodes as a diffused dischargeof several different types all of lesser intensity than that which iscommonly associated with arcs. It is also well known that a portion ofthe discharge including the arc can be altered by the use of magneticfields.

It has been found in tests with high speed motion picture studies ofcurrent fiow between an electrode such as that described and claimed inUS. Pat. No. 3,368,018 issued Feb. 6, 19.68 to S. M. DeCorso et al. forElectrode and Tip" and assigned to the assignee of the instantinvention, and a molten metal pool in a vacuum melting furnace equipedwith an external solenoid that the electric discharge consisted of alarge diameter diffused column. This column extended across the diameterof the molten pool at its lower end and across a substantial part of theelectrode base at its upper end roughly centered on the electrode axis.The edge of the column was curved in such a manner as to suggest that itconformed to flux lines of the combined magnetic field generated byfield coil in the electrode and the furnace solenoid.

In the operation of such an electrode without a furnace solenoid atatmospheric pressures, an intensely hot concentrated arc is movedrapidly over the electrode surface by its interaction with thecomponents of a magnetic field parallel to the electrodes surface. Thismotion distributes the heat flux from the arc route to the electrodesover a large area to prevent local overheating and consequent electrodedamage. The normal magnetic field relation of a field generated by acoil in the electrode to the arcing surface of the electrode is shown inFIG. 1B illustrating the prior art.

For a large diameter diffused are which is generally coaxial with theelectrode axis and the type of magnetic field generated by a field coilin the electrode, as described, the induced motion consists of rotationof the discharge column about the common axis without a change in thearea of the arcing surface of the electrode which is subjected to heatflux. As long as the arc is diffused enough, local heat flux to theelectrode will be sufficiently low to prevent electrode damage. However,an increase in the electrical current in the are or a decrease in thediameter of the diffused arc may burden the capacity of the electrodecooling system beyond its capability to remove heat flux resulting inerosion of the electrode surface by melting or vaporization.

As previously stated, my invention proposes to control, and shows anumber of embodiments of apparatus for controlling, the unit flux to acooled electrode and the material being treated by a diffused arc columnoperating at a given electric current level, by means of a shapedmagnetic field, the field being generated by means which by itself wouldproduce a magnetic field with the magnetic field lines coaxial with theelectrode, the electrode itself including means for distorting thegenerated magnetic field and shaping it in a manner to facilitateoperation of the furnace to prolong the life of the electrode. Theobjects of my invention are accomplished by shaping the field andcontrolling the flux lines which pass through both the cooled electrodesur face and the molten bath, and further by controlling the portion ofthe total area of the arcing surface on which the flux lines impinge aswell as controlling the portion or portions of the arcing surface onwhich the flux lines impinge where this is desirable to improve theoperation of the apparatus. An example of a magnetic field generated bya solenoid adjacent the wall of a furnace with an electrode in thefurnace having an axis substantially coaxial with the axis of thesolenoid is shown in FIG. 1A without any shaping or distortion of thesolenoid field by means within the electrode. In an electrode such asshown in FIG. 1A having no means to generate a field, and no means todistort a field, and operating within an area where a magnetic field isgenerated by a solenoid, the motion of electrified particles isunimpeded along flux lines and restricted perpendicular to them,electrified particles emanating at either the electrode or bath tend tobe confined along lines of flux passing through both. The general typeof field shown in FIG. 1A is used to provide in vacuum metal meltingfurnaces stirring action in the molten pool, such for example as theapparatus shown and described in U.S. Pat. No. 3,108,151 issued Oct. 22,1963 to Garmy et al. for Electric Furnace." The field in FIG. 1A of thispatent and generally in the prior art is produced by a solenoid externalto the electrode and external to the means enclosing the working volumeof metal.

My invention resides at least in part in the discovery that anexternally produced magnetic field generally coaxial with the electrodecan be distorted locally by means within the electrode to change theeffective electrode surface area and the melt or bath surface areaintercepted by a given set of flux lines.

FIGS. 2A and 2B show means for distorting the magnetic field in whichthe electrode tip is composed of high permeability material, the tip ofFIG. 2A having on the inside and outside diameter thereof amounts ofhigh permeability material not greatly different from each other, thetip of FIG. 2B having a considerably greater amount of high permeabilitymaterial on its outside surface than it does on its inside surface sothat the tip of FIG. 2B is referred to herein as an outside diameterbiased electrode tip.

As seen from the Figures, a tip constructed according to theillustration of FIG. 2A gives substantially uniform arc distributionover the whole bottom surface of the tip, which bottom portion may inthat case consist of, in effect, the entire arcing surface; on the otherhand the tip of FIG. 2B, while increasing the flux deni sity along thebottom surface of the electrode tip, also distorts the magnetic field ofthe solenoid so that flux lines extending between the melt and theelectrode impinge on the outside wall of larger diameter of theelectrode, the last-named wall portion then becoming in some cases partof the arcing surface.

Particular reference is made to FIGS. 2C and 2D where shaping ordistortion of the field is produced by high permeability materiallocated within the electrode. With reference to shaping of the field asshown in FIG. 2C, it is seen that as may be expected flux lines emergingfrom the melt tend to converge toward the ring of high permeabilitymaterial 54 in the electrode and in effect there is some concentrationof flux over a predetermined portion of the arcing surface of the tip.The flux concentration on the tip in FIG. 2C is strongest at a radialposition corresponding to the mean diameter of high permeability ring54, and the magnetic field is weakest at any point measured on eitherthe inside or outside surface of the tip which has an axial positioncorresponding to the midpoint of ring 54 taken in an axial direction. 7

Particular reference is made to FIG. 2D where there is not only highpermeability material within the tip but a substantial volume of highpermeability material is located within the electrode supporting columnand extends axially upward well beyond the tip. It is seen from themagnetic field pattern of FIG. 2D that flux lines of the field extendingbetween the melt and the electrode not only converge toward the bottomof the tip but are also caused to converge toward the outer wall of theelectrode tip; the effect of the electrode tip construction shown inFIG. 2D is to distribute the flux lines on a larger portion of the totalarea of the arcing surface of the tip, allowing that portion of thecooling fluid in the passageway in the tip to conduct heat flux from alarger portion of the total area of the arcing surface of the tip,thereby reducing the requirement for minimum heat flux removalcapability.

Particularreference is made now to FIGS. 3A and 38 where the magneticfield of the solenoid is distorted by a permenent magnet located withinthe tip of the electrode. In FIG. 3A the magnetic fields of the solenoidand the permanent magnet within the tip are of such a polarity that theyadd to each other with the result that there is an increase in fluxlines converging on the arcing surface of the electrode adjacent thepermanent magnet.

In FIG. 3B the field generated by the permanent magnet in the tip is ofsuch a polarity that it opposes the magnetic field generated by thesolenoid. The field configuration of FlG. 3B tends to bring the are upthe core or center of the electrode. It will be noted that in the areagenerally designated X in the drawing the flux is substantially zero andthere could be an arc path between the melt and the electrode passingthrough the area designated X.

Particular reference is made to FIGS. 4A and 4B. In the electrodeillustrated in both of these figures a permanent magnet is locatedwithin the electrode tip, the permanent magnet consisting of a ring witha generally axially extending inner wall of smaller diameter and agenerally axially extending outer wall of larger diameter and themagnetic poles of the permanent magnet in both cases are on the insideand outside walls of the permanent magnet. The field illustrated in FIG.4A generated by the solenoid has a north to south polarity in which thenorth pole lies at the upper end of the field illustrated, while thesouth pole lies at the lower end portion of the field illustrated, andthe permanent magnet within the tip has its south magnetic pole formedby the inside surface of smaller diameter and its north magnetic poleformed by the outside surface of larger diameter. The magnetic fieldconfiguration shown in FIG. 4A tends to concentrate the arc andconsequently the heat generated by the are spot on the bottom or faceand on the inside diameter or inside surface of the electrode tip.

In the figure illustrated in FIG. 4B the field of the solenoid has asimilar polarity to that shown in FIG. 4A, but the polarity of thepermanent magnet within the tip is reversed and in FIG. 4B the outsidesurface of larger diameter constitutes the south magnetic pole of thepermanent magnet while the inside surface of smaller diameter forms thenorth magnetic pole of the permanent magnet. It is seen from FIG. 48that the resultant magnetic field tends to concentrate flux lines on theface or bottom and on the outside diameter of the electrode tip with aresulting effect that the are tends to occur predominately from these"portions of the arcing surface and most of the heat flux removal bycooling fluid in the tip from these portions of the arcing surface ofthe electrode.

It is seen then that the various embodiments of my invention providegreat versatility in determining the portion of the total area of thearcing surface upon which the arc can be expected to impinge and alsoprovide great versatility in limiting the arc to a certain desiredportion of the arcing surface, or in utilizing certain' desired portionsof the arcing surface of the tip to utilize the maximum heat fluxtransfer capabilities of the electrode, to concentrate the are on themelt within the furnace in accordance with flux lines extending betweenthe electrode and the melt, to stir the melt, and to prevent undesirablemodes of operation of the are from the electrode.

Indicated positions of permanent magnets and ferromagnetic parts withinthe electrode envelope should not be interpreted to mean that theseelements are permanently fixed in position. Where advantageous forspecific conditions during a portion of a melting cycle, these elementscould be hydraulically or mechanically moved within the confines of theelectrode envelope to provide a variable flux condition for a fixedarcing distance between electrode tip and melt.

I claim as my invention:

1. Furnace apparatus including a furnace having a wall, said furnaceadapted to contain at least partially electrically conductive materialto be melted, an electrode including means forming an arcing surfacemounted in the furnace in a position therein substantially perpendicularto the surface of the melt, electrical circuit means connected to theelectrode and to the melt for producing and sustaining an arctherebetween, the are extending substantially parallel to thelongitudinal axis of the electrode, material having a high permeabilitymounted in the electrode near the arcing surface, and means near thewall of the furnace for setting up a magnetic field having a componentin the furnace substantially parallel to the axis of the electrode andperpendicular to the surface of the melt, said high permeabilitymaterial attracting lines of force of said magneticfield and causing aconcentrated field at the arcing surface extending'between the arcingsurface and the melt, said concentrated field focusing the are betweenthe electrode and the melt thereby preventing flaring of the arc towardthe inside wall of the furnace.

2. Furnace apparatus adapted to have a melt of at least partiallyelectrically conductive material, comprising an electrode electriccircuit means connected to the electrode and the melt for producing andsustaining an arc therebetween, means near the furnace wall forgenerating a magnetic field having a component extending between themelt and the electrode, means in the electrode effective withoutrequiring energizing power for increasing the strength of the componentof the magnetic field to thereby focus the are.

3. Furnace apparatus comprising means for containing a melt which is atleast partially electrically conductive, an electrode disposed inpredetermined spaced relationship with the melt, the electrode and themelt being adapted to be connected to terminals of opposite polarity ofa source of potential to produce and sustain an are between theelectrode and the melt, means disposed close to the wall of thecontaining means for generating a magnetic field within the containingmeans and adjacent at least a portion of the electrode which extendsaxially between the electrode and the melt, the electrode includingmeans effective without requiring energizing power for causing at leastsome of the magnetic field lines to depart in a desired manner frompaths which they would normally tend to follow.

4. Apparatus according to claim 3 in which the electrode has meansforming an arcing surface and in which the means for causing at leastsome of the magnetic field lines to depart from their normal paths isutilized for controlling the percentage of the total area of the arcingsurface upon which said are impinges.

5. Apparatus according to claim 3 in which the electrode includes meansforming an arcing surface and in which the means within the electrodefor causing at least some of the magnetic field lines to depart fromtheir normal paths is utilized to concentrate magnetic field lines insuch a manner that an increased number enter or pass through said arcingsurface than would so do were said latter means not present in saidelectrode.

6. Furnace apparatus comprising means for containing a melt which is atleast partially electrically conductive, an electrode disposed inpredetermined spaced relationship with the melt, the electrode and themelt being adapted to be connected to terminals of opposite polarity ofa source of potential to produce and sustain an are between theelectrode and the melt, means disposed close to the wall of thecontaining means for generating a magnetic field within the containingmeans and adjacent at least a portion of the electrode which extendsaxially between the electrode and the melt, the electrode includingmeans effective without requiring energizing power for causing at leastsome of the magnetic field lines to depart in a desired manner frompaths which they would normally tend to follow, the electrode beingadditionally characterized as having a tip forming an arcing surface,the tip being generally annular in a horizontal plane and generallyU-shaped in vertical plane cross section along any radius with a spacetherein extending around the entire tip, said means for causing at leastsome of the magnetic field lines to depart from their normal pathsdisposed within the space and composed of high permeability material.

7. Furnace apparatus comprising means for containing a melt which is atleast partially electrically conductivc, an electrode disposed inpredetermined spaced relationship with the melt, the electrode and themelt being adapted to be connected to terminals of opposite polarity ofa source of potential to produce and sustain an are between theelectrode and the melt, means disposed close to the wall of thecontaining means for generating a magnetic field within the containingmeans and adjacent at least a portion of the electrode which extendsaxially between the electrode and the melt, the electrode includingmeans effective without requiring energizing power for causing at leastsome of the magnetic field lines to depart in a desired manner frompaths which they would normally tend to follow, the electrode beingadditionally characterized as including a supporting column with a tip,the supporting column including means forming a generally cylindricalspace of at least a predetermined width, and the means for causing atleast some of the magnetic field lines to depart from their normal pathsis generally annular and disposed within the space and composed of highpermeability material.

8. Furnace apparatus comprising means for containing a melt which is atleast partially electrically conductive, an electrode disposed inpredetermined spaced re-- lationship with the melt, the electrode andthe melt being adapted to be connected to terminals of opposite polarityof a source of potential to produce and sustain an are between theelectrode and the melt, means disposed close to the wall of thecontaining means for generating a magnetic field within the containingmeans and adjacent at least a portion of the electrode which extendsaxially between the electrode and the melt, the electrode includingmeans effective without requiring energizing power for causing at leastsome of the magnetic field lines to depart in a desired manner frompaths which they would normally tend to follow, the electrode beingadditionally characterized as including a supporting column with a tip,the tip having a space therein extending around the tip, the columnhaving means fonning a generally cylindrical space of at least apredetermined width, the space in the tip being radially aligned withthe space in the column, the spaces opening into each other, the meansfor causing at least some of the magnetic field lines to depart fromtheir normal paths being generally annular and composed of highpermeability material occupying at least one of the spaces within thecolumn and the tip.

9. Apparatus according to claim 8 in which the high permeabilitymaterial occupies both the space within the tip and at least a portionof the space within the column.

l0. Furnace apparatus adapted to have a melt of at least partiallyelectrically conductive material, comprising an electrode spaced fromsaid melt, electric circuit means connected to the electrode and themelt for producing and sustaining an arc therebetween, at least oneelement for generating a magnetic field, at least one other element aspart of the electrode being effective without requiring energizingpower, the first and second elements cooperating with each other toproduce a resultant magnetic field pattern which is shaped anddimensioned to control at least one of the operating parameters of thefurnace apparatus including the total area on the electrode surface fromwhich the arc takes place, the particular portion of the electrodesurface from which the arc takes place, the total area of the surface ofthe melt upon which the arc impinges, the particular portion of thesurface of the melt upon which the arc impinges.

1. Furnace apparatus including a furnace having a wall, said furnaceadapted to contain at least partially electrically conductive materialto be melted, an electrode including means forming an arcing surfacemounted in the furnace in a position therein substantially perpendicularto the surface of the melt, electrical circuit means connected to theelectrode and to the melt for producing and sustaining an arctherebetween, the arc extending substantially parallel to thelongitudinal axis of the electrode, material having a high permeabilitymounted in the electrode near the arcing surface, and means near thewall of the furnace for setting up a magnetic field having a componentin the furnace substantially parallel to the axis of the electrode andperpendicular to the surface of the melt, said high permeabilitymaterial attracting lines of force of said magnetic field and causing aconcentrated field at the arcing surface extending between the arcingsurface and the melt, said concentrated field focusing the arc betweenthe electrode and the melt thereby preventing flaring of the arc towardthe inside wall of the furnace.
 2. Furnace apparatus adapted to have amelt of at least partially electrically conductive material, comprisingan electrode electric circuit means connected to the electrode and themelt for producing and sustaining an arc therebetween, means near thefurnace wall for generating a magnetic field having a componentextending between the melt and the electrode, means in the electrodeeffective without requiring energizing power for increasing the strengthof the component of the magnetic field to thereby focus the arc. 3.Furnace apparatus comprising means for containing a melt which is atleast partially electrically conductive, an electrode disposed inpredetermined spaced relationship with the melt, the electrode and themelt being adapted to be connected to terminals of opposite polarity ofa source of potential to produce and sustain an arc between theelectrode and the melt, means disposed close to the wall of thecontaining means for generating a magnetic field within the containingmeans and adjacent at least a portion of the electrode which extendsaxially between the electrode and the melt, the electrode includingmeans effective without requiring energizing power for causing at leastsome of the magnetic field lines to depart in a desired manner frompaths which they would normally tend to follow.
 4. Apparatus accordingto claim 3 in which the electrode has means forming an arcing surfaceand in which the means for causing at least some of the magnetic fieldlines to depart from their normal paths is utilized for controlling thepercentage of the total area of the arcing surface upon which said arcimpinges.
 5. Apparatus according to claim 3 in which the electrodeincludes means forming an arcing surface and in which the means withinthe electrode for causing at least some of the magnetic field lines todepart from their normal paths is utilized to concentrate magnetic fieldlines in such a manner that an increased number enter or pass throughsaid arcing surface than would so do were said latter means not presentin said electrode.
 6. Furnace apparatus comprising means for containinga melt which is at least partially electrically conductive, an electrodedisposed in predetermined spaced relationship with the melt, theelectrode and the melt being adapted to be connected to terminals ofopposite polarity of a source of potential to produce and sustain an arcbetween the electrode and the melt, means disposed close to the wall ofthe containing means for generating a magnetic field within thecontaining means and adjacent at least a portion of the electrode whichextends axially between the electrode and the melt, the electrodeincluding means effective without requiring energizing power for causingat least some of the magnetic field lines to depart in a desired mannerfrom paths which they would normally tend to follow, the electrode beingadditionally characterized as having a tip forming an arcing surface,the tip being generally annular in a horizontal plane and generallyU-shaped in vertical plane cross section along any radius with a spacetherein extending around the entire tip, said means for causing at leastsome of the magnetic field lines to depart from their normal pathsdisposed within the space and composed of high permeability material. 7.Furnace apparatus comprising means for containing a melt which is atleast partially electrically conductive, an electrode disposed inpredetermined spaced relationship with the melt, the electrode and themelt being adapted to be connected to terminals of opposite polarity ofa source of potential to produce and sustain an arc between theelectrode and the melt, means disposed close to the wall of thecontaining means for generating a magnetic field within the containingmeans and adjacent at least a portion of the electrode which extendsaxially between the electrode and the melt, the electrode includingmeans effective without requiring energizing power for causing at leastsome of the magnetic field lines to depart in a desired manner frompaths which they would normally tend to follow, the electrode beingadditionally characterized as including a supporting column with a tip,the supporting column including means forming a generally cylindricalspace of at least a predetermined width, and the means for causing atleast some of the magnetic field lines to depart from their normal pathsis generally annular and disposed within the space and composed of highpermeability material.
 8. Furnace apparatus comprising means forcontaining a melt which is at least partially electrically conductive,an electrode disposed in predetermined spaced relationship with themelt, the electrode and the melt being adapted to be connected toterminals of opposite polarity of a source of potential to produce andsustain an arc between the electrode and the melt, means disposed closeto the wall of the containing means for generating a magnetic fieldwithin the containing means and adjacent at least a portion of theelectrode which exteNds axially between the electrode and the melt, theelectrode including means effective without requiring energizing powerfor causing at least some of the magnetic field lines to depart in adesired manner from paths which they would normally tend to follow, theelectrode being additionally characterized as including a supportingcolumn with a tip, the tip having a space therein extending around thetip, the column having means forming a generally cylindrical space of atleast a predetermined width, the space in the tip being radially alignedwith the space in the column, the spaces opening into each other, themeans for causing at least some of the magnetic field lines to departfrom their normal paths being generally annular and composed of highpermeability material occupying at least one of the spaces within thecolumn and the tip.
 9. Apparatus according to claim 8 in which the highpermeability material occupies both the space within the tip and atleast a portion of the space within the column.
 10. Furnace apparatusadapted to have a melt of at least partially electrically conductivematerial, comprising an electrode spaced from said melt, electriccircuit means connected to the electrode and the melt for producing andsustaining an arc therebetween, at least one element for generating amagnetic field, at least one other element as part of the electrodebeing effective without requiring energizing power, the first and secondelements cooperating with each other to produce a resultant magneticfield pattern which is shaped and dimensioned to control at least one ofthe operating parameters of the furnace apparatus including the totalarea on the electrode surface from which the arc takes place, theparticular portion of the electrode surface from which the arc takesplace, the total area of the surface of the melt upon which the arcimpinges, the particular portion of the surface of the melt upon whichthe arc impinges.